This invention relates to certain copper toxicants and the dissemination of them in a sustained and controlled manner to destroy disease spreading trematode hosts. It is well known that various molluscan species, such as snails, serve as hosts to trematode parasites which infect both man and lower animal species with various diseases. Man can be infected with debilitating Shistosomiasis from various trematode parasites including S. hematobium, S. mansoni, S. japonicum, and S. dermatitis. Other trematodes are causative agents of Fascioliasis, a disease which effects various animals such as domestic horses, cattle and sheep.
Control of the diseases caused by trematodes, such as Shistosomiasis and Fascioliasis, have been conventionally done through medical programs, sanitary engineering and chemical treatment. Medical programs are expensive to the point of being out of economic reach for most of the affected areas. Further, although various drugs are known which will stop the infection within an individual, the treatment cannot stop the disease causing cycle in that immunity cannot be conferred and the "cured" individual usually becomes reinfected upon reexposure to the trematode-infected waters. Sanitary engineering, including sanitary facilities, water purification, concrete lined irrigation canals, etc., are also far too expensive to undertake on the massive scale which is required.
The primary method of controlling diseases carried by the various trematodes is the destruction of the host molluscan by the application of chemical agents to the infected area, such as a waterway. These molluscicides, include copper salts, sodium pentachlorophenate, N-trityl-morphine, niclosamide salts and organo tin compounds, are applied to the infested waterways as solutions, emulsions, wettable powders or granules in conventional manners. The treated water bodies are toxic for only short periods of time due to the nonpersistent nature of the molluscicide toxicant which chemically interact with dissolved minerals and gases, are absorbed by suspended matter, and undergo biodegradation. Molluscicide effective life is further shortened in flowing water systems by the dilution of fresh water inflow. The relatively low effective life of the molluscicide toxicant requires frequent application of massive dosages of the toxicant material. Although such treatment effectively destroys the host molluscan it is also detrimental to piscine life and other nontarget elements of the biota. Further, it is known that the target molluscans are capable of detecting the toxicants at the high level used and are able to evade mortality by burrowing in the mud or leaving the treated water body, and returning after detoxification to reinfest the now cleared waterway. The net result is the necessity for systematic, periodic retreatment.
Various compounds, including those of copper, have also been previously used as a pesticide to control undesired aquatic plant life. The conventional application of large dosages of these compounds has known detrimental effects on desired plant and animal life as discussed above.
Slow releasing toxicant compositions are presently known which have a long term biocidal effectiveness. While conventional treatment results in acute intoxification and rapid mortality of the target as well as other aquatic life, the slow release toxicant compositions are able to establish a constant level of intoxification of the water body leading to mortality of the target through subacute or chronic manifestations. The slow releasing toxicant compositions, such as those taught in U.S. Pat. Nos. 3,639,583; 3,417,181; and 3,767,809, utilize various organic toxicants, including organo tin and organo phosphorus compounds. These compositions consist of toxicant-elastomeric matrix which have certain solubility relationships which allow for the slow loss of the toxicant into the surrounding waters through a diffusion-dissolution mechanism. The long term action provided by these known compositions results from the physical mechanism of solubility equilibrium and requires that the toxicant agent be soluble in the elastomeric material utilized. The toxicant release is thereby governed by a solubility equilibrium wherein the loss of toxicant material near the elastomeric matrix surface-water interphase leads to solution disequilibrium within the matrix and the migration of the internal molecules of elastomer-soluble toxicant toward the depleted surface area. The net result is a continuous loss of toxicant in accordance with the classical diffusion principles. These toxicant compositions have the drawback of being limited to toxic materials which are soluble in the elastomeric matrix and relatively insoluble in water. Such toxic materials are relatively expensive and may present a human health hazard in their formation, handling and use.
Copper compounds have been previously utilized as a pesticidal agent and more specifically as a molluscicide. The copper compounds are preferred over various other known molluscicide materials due to their relatively low cost and low toxic properties to humans but when presently utilized require frequent application of large dosages to be effective. The present copper toxicants have heretofore not been found useful in sustained release application because of their known insolubility in the elastomeric matrixes.